I found that converting your input cell to TraditionalForm and then back again to StandardForm - thus causing the terms in the differential equations to be reorganised - made NDSolve work though you now get a "NDSolve::mxst: Maximum number of 10000 steps reached ..." warning message.

Stephen LuttrellWest Malvern, UK

On Thursday, 6 December 2012 09:56:30 UTC, hazem.ab...@gmail.com wrote:> Dear all,>> I want to solve this system of equations but I always get an error>>>> NDSolve::ndnum:Encountered non-numerical value for a derivative at t==0>>>> can any one help me on this>>>> s=NDSolve[{>> ph1''[t]+ph1'[t]+sin[ph1[t]]-mu[t]-mu'[t]==0.005,>> ph2''[t]+ph2'[t]+sin[ph2[t]]+mu[t]+mu'[t]==0.005,>> 0.2mu'[t]+mu[t]==ph1'[t]-ph2'[t],>> ph2[0]==0,>> ph1[0]==0,>> ph2'[0]==0,>> ph1'[0]==0,>> mu[0]==0>> },>> {ph1[t],ph2[t],mu[t]},>> {t,0,5000}>> ]>>>> thanks in advance,